The inventive concepts disclosed herein relate generally to the field of distortion correction for a head up display (HUD) in an aircraft. A HUD may be used by an operator in an aircraft to allow the operator to have a view of the outside world with superimposed information, such as symbols and images captured by sensors.
Worn HUDs including but not limited to head worn displays (HWDs), such as, helmet mounted displays (HMDs), are used in aircraft applications, both in in-flight applications and in flight simulators. Head worn displays include monocular type displays having a single display area (viewable by one or two eyes) and binocular type displays having separate left and right eye display areas. With a binocular type display, the left eye sees a left eye image display while the right eye sees a right eye image display.
Monocular and binocular displays generally include a distortion map that is used to correct optical distortion. In binocular type displays, the distortion is corrected in the left eye display image and the right eye display image provided by the worn display, such as, an HMD. Generally, the distortion map is generated using a test fixture and one or more test cameras prior to the HMD entering service. The test fixture can include collimating devices, such as telescopes for the eye positions and the camera on the HMD. The test cameras are placed at the expected eye positions and capture test images projected on the left eye image display and the right eye image display. The distortion map is calculated based upon the test fixture camera data.
Distortion after the distortion map is generated can be introduced into the HMD due to creep in mechanical tolerances (e.g., the sizes, spacing, and shapes of optical components change over time, thereby introducing new distortion into the system). Less expensive, flexible molded composite components (e.g., visor/combiners, etc.) can be particularly prone to creep. Conventional HMDs require that an HMD exhibiting excessive distortion due to mechanical creep be returned to the manufacturer for calibration or re-characterization with a new distortion map using the test fixture and camera. Returning the HMD to the manufacturer is expensive and time consuming. Further, using the test fixture with the test cameras at the expected eye position does not allow the HMD to be characterized with respect to a particular user of the HMD.